The present invention generally relates to a laser apparatus which uses a binocular indirect ophthalmoscope fixedly mounted on the head of an operator and, more particularly, to an apparatus which is suitable for photocoagulation treatment of the peripheral portion of a patients fundus oculi.
In fundus disease treatments, there has been conventionally used a photocoagulation apparatus which is using an argon laser for photocoagulation treatment. Such a photocoagulation apparatus generally has had defects that the main device of the apparatus is large in size, a positional relationship between the apparatus and a patient's eye is substantially fixed to provide a poor handleability, a manipulator type apparatus requires an operator to use an experienced assistant in operating the apparatus, and so on.
For the purpose of solving these problems, JP-A-57-78852 discloses an apparatus wherein a beam emitted from a photocoagulation light source is guided to a binocular indirect ophthalmoscope via an optical fiber to attain a coaxial relationship with respect to an illumination optical system.
Further, in order to overcome problems caused by the large size of such laser apparatuses, there have recently been suggested laser apparatuses which use a beam emitted from a small sized semiconductor laser diode for treatment, as in JP-A 1-236070, 1-236071 and 1-236050.
With the laser apparatus of the JP-A 57-78852, a photocoagulation optical system and an illumination optical system are set to have a mutual coaxial relationship but to be shifted in its optical axis from the optical axis of an observation system. For this reason, even when an operator is observing a patient's fundus, it is difficult for the operator to judge whether or not a treatment beam is shut off by patient's pupil. Therefore, such a laser apparatus has been defective in that, in a treatment requiring a predetermined level of beam power, when the operator cannot perform the treatment because of its insufficient power, it is hard for the operator to judge whether the impossible treatment results from the treatment beam shut off by the patient's pupil or from the deterioration of the apparatus itself. Further, when such a laser emitting a beam of a large divergence angle as a semiconductor laser is employed, a beam passing through the pupil becomes diverged correspondingly widely and thus the amount of beam shut off by the iris becomes also large. Furthermore, since the semiconductor laser emits a beam with a wavelength of about 800 nm, the absorption of the beam at the fundus is low. In addition, output power transmitted by a binocular indirect ophthalmoscope is relatively small, and the shut-off of the beam at the iris disadvantageously tends to cause an insufficient power. Conversely, when the output is adjusted while the laser beam is shut off by the iris or the like so that the laser beam is irradiated at such a position as immune to such shut-off, the power may become too strong.